The following has been written for the August / September issue of the Binfield Beacon. If you want to read a longer version then have a look at https://ecoworrier133969581.wordpress.com/2020/07/07/come-on-you-blues/
In my opinion, one of Bracknell’s most beautiful residents is the silver-studded blue butterfly. The male of this heath-land specialist has iridescent blue upper-wings. Both the male and female have silvery-blue patches on their hind wings that give them their name, and a beautiful pattern on their under-wings that distinguishes them from other kinds of blue butterfly.
This butterfly also has a rather incredible life-story. The female lays her eggs on heather, or other similar plants, in relatively sheltered areas. When they hatch, the caterpillars quickly fatten-up by eating these plants. Once they have grown, the caterpillars start to produce a milky secretion that is attractive to black ants (another heath-land specialist). The ants carry the caterpillar into their nests providing it with protection from birds, mammals and reptiles. In the nest, the caterpillar turns into a chrysalis. Peter Marren, in his lovely book ‘Rainbow Dust’, writes “One of the most amazing sights of the butterfly world, one discovered only recently, is the emergence from the ant’s nest of a Silver-studded Blue butterfly with anything up to eight ants frantically licking its body. The hour which every butterfly has to spend drying its wings is perhaps the most vulnerable of its whole life. But with a posse of fierce ants to stand guard, the chances of survival are much greater.”
So, silver-studded blues need sunny heath-land sites sheltered by scrub, the presence of black ants, and for the heather to be kept relatively short, for example by rabbits. They also tend to live their entire lives within about 20m of the ant-nest from which they emerged, so any damage to that area of heath could wipe out an entire colony.
The UK supports about a fifth of the lowland heath in Europe, but the UK had about 5 times as much lowland heath in the 1800s. Berkshire, which is one of the counties that still has lowland heath, and silver-studded blue butterflies, had about 50 times as much in the 1800s. Bracknell Forest has about a third of Berkshire’s lowland heath. This rare habitat is currently given the highest possible level of protection. Although some heath-land restoration has happened in the last twenty years, the pressure on lowland heath in this area remains high.
The best time to see silver-studded blues is on a still warm day during June or July. In perfect conditions, clouds of hundreds of butterflies can be found over a relatively small patch of heather. If you are lucky enough to see one then take the time to inspect it closely.
If you want a simple guide to identifying butterflies, then I recommend the Field Studies Council’s ‘Guide to the butterflies of Britain and Ireland’. If you want to know more about butterflies and the history of the people who named them, collected them and painted them then read ‘Rainbow Dust’ by Peter Marren.